1. Field of the Invention
The invention relates to a process for separating tin as well as, if required, copper from scrap melts, in particular, tinplate melts or metal-oxide-containing combustion residues.
2. Description of the Related Art
In the course of the working up of waste or of metal-oxide-containing combustion residues or slags, purification processes have already been proposed in which the slags are purified while forming an iron bath or by using an iron bath. Depending on the composition of the starting slags, such melts occurring as pig iron baths, contain more or less high portions of copper. However, copper contained in pig iron and, in particular, steel constitutes a metallurgical problem. Copper interferes with the production of flat products, such as, for instance, deep-drawing sheets. Steel works most frequently process only steel grades that must have copper contents of less than 0.1%. With longitudinal products, for instance beams and girders, structural steels or rails, slightly higher copper contents are admissible, though. Yet, also there the upper limit of the copper content most frequently is less than 0.4% by weight. Copper is introduced via scrap also in steel production processes, the amount of copper contained in steel increasing with the scrap recycling rate being raised.
From EP-707083 a process for working up waste or metal-oxide-containing metallic combustion residues has already become known, in which reduction was carried out after an at least partial oxidation of the melt to slag under separation of a metal bath. In the course of reduction, which may be effected, for instance, by blowing in carbon monoxide/carbon dioxide, copper is introduced into the iron bath, whereby nonferrous heavy metals may subsequently segregate in the form of crude bronze. After the segregation of crude bronze at a temperature of about 1500.degree. C., crude copper having an iron content of approximately 4% by weight was formed, as a rule, yet relatively high contents of copper continued to remain within the iron bath. The remaining iron alloy typically contains approximately 8% by weight of copper.
From WO 96/24696 a process for producing pig iron or steel and cement clinker from slags has become known, in which a ferrite slag is formed and likewise is reduced in a reduction reactor while forming an iron bath and, in the sinter phase, while burning carbon. As in the first-mentioned process, the pig iron bath may subsequently be refined, it being possible that copper contents too high for a number of further applications remain in the steel. Even iron baths specifically employed for refining slags and, in particular, pig iron baths contain more or less high copper contents depending on the case histories of the slags.
Another problem of such metallic melts resides in their high contents of tin.
The tin content of steel usually ranges between 0.015 and 0.02% by weight in the steel. By extrapolation to scrap, tin contents of 0.1% by weight will, however, result, the presence of tin in such high amounts after scrap melting leading to products capable of being utilized to a limited extent only. This will apply all the more if tin plate melts are produced and, therefore, a simple and reliable process for separating tin is of substantial economic importance in order to obtain economically utilizable melting products.
Scrap melting processes and, in particular, tinplate melts, as a rule, hitherto have brought about products that may be utilized to a limited extent only and are no longer suitable for a number of applications. A tin content of above 500 ppm will result in markedly reduced strength and deformation properties of the product such that a simple and safe process or separating tin may substantially enhance the value of the melting product.